Two Greek words are used for 'to know' in the New Testament -- ginosko and oida. The former signifies objective knowledge, what a man has learned or acquired. The English expression 'being acquainted with' perhaps conveys the meaning. Oida conveys the thought of what is inward, the inward consciousness in the mind, intuitive knowledge not immediately derived from what is external. The difference between the two words is illustrated in John 8.55, 'ye know (ginosko) him not; but I know (oida) him;' in John 13.7, 'What I do thou dost not know (oida) now, but thou shalt know (ginosko) hereafter;' and in Heb. 8.11, 'they shall not teach ... saying, Know (ginosko) the Lord; because all shall know (oida) me.' The word oida is used of Christ as knowing the Father, and as knowing the hypocrisy of the Scribes and Pharisees, of Paul's knowledge of a 'man in Christ,' and of the Christian's knowledge that he has eternal life. 'I know whom I have believed,' 2Tim. 1.12 -- I have the inward conscious knowledge of who the person is: see also 1Cor. 16.15; 2Tim. 3.14 and 15 -- all of these refer to inward conscious knowledge. The difference between the significance of the two words is often slight; and objective knowledge may pass into conscious knowledge, but not vice versa. The Greek for conscience is derived from oida: see ch. 4.4, 'I am conscious of nothing in myself,' that is, not conscious of any fault. In the present passage, 'We know that an idol is nothing' is conscious knowledge: 'we all have knowledge' and 'knowledge puffs up' is objective knowledge. 'If any one think he knows (conscious knowledge), he knows (objectively) nothing yet as he ought to know it (objectively):' 'he is known (objectively) of him,' so 'knowledge,' ver. 10.